Finishing of polyamide fabrics



Dec. 26, 1944'. v E B, BENGER v2,365,931

FINISHING OF POLYAMIDE FABRICS Filed Feb. 13, 1941 /DoZyam i078 Fa Znrz'c f1 r; C/

EFHEEB- Belge? Patented Dec. 26, 1944 `FINISHING F POLYAMIDE FABRICS Ernest B. Benger, Wilmington, Del., assignoi to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application February 13, 1941, Serial No. 378,835

9 Claims.

This invention relates to textile fabrics and more particularly to a process for improving `the resilience of fabrics .prepared from synthetic linear polymer bers.

The fabrics with which this invention are concerned are prepared from bers made of synthetic linear polyamid'sfof the general type described ln U. S. 2,071,250, 2,071,253 and 2,130,948. These polyamides are high molecular weight polymers which are generally crystalline in structure and which are capable of being cold drawn into fibers showing by characteristic X-ray patterns molecular orientation along the ber axis. Generally speaking. these synthetic linear polyamides comprise reaction products of a polyamide-forming composition in which the molecules are bi-` functional and contain two amide-forming groups, each of which is complementary to an amide-forming group in other molecules in said composition.

The polyamides defined above or as otherwise identified hereinafter can be obtained, for example, by self-polymerization of monoaminomonocarboxylic acids, or by reacting diamines `with dibasic carboxylic acids in substantially equimolecular amounts, it being understood that reference herein to the amino acids, rdiamines, and dibasic carboxylic acids is intended to include the equivalent amide-forming derivatives thereof. In the case ofthe amino acids these derivatives include substances such as/ the ester, amide. lactam, n-formyl derivatives, and, when water is present, the nitrile; in the case of the diamines they include the carbamates and the N-formyl and N,Ndiformyl derivatives; and in the case of the dibasic carboxylic acids they include the diester, monoester, anhydride, amide, acid halide,

and, when water is present, the monoand di- 'nitrile/s.

These polyamides include also polymers obtained by including with the polyamide-forming reactants other l'linear polymer-forming reactants, e. g., glycols, monohydroxymonocarboxylic acids, and monoaminomonohydric alcohols. lIt should be noted that in the polyamides of this invention the amide group is an integral ypart of the main chain of atoms' in the polymer these fibers have thus far shown little promise because they have poor hand and are deficient in resilience, that is, they do not have vthe life or springiness of fabrics made from natural fibers such as silk and wool. They are also deficient in hand and drape.

It is also known that fabrics made from natural fibers, such as cotton, silk and wool, and from artificial cellulosic fibers are given finishing `treatments which improved their hand, appearancey and other properties. Such treatments comprise subjecting the fabrics to the'action of warm or hot soap solutions with or without various mechanical treatments. Application of such treatments to the synthetic linear polyamide fabrics produces little or no improvement in resiliency or hand.

It has been proposed to improve the properties of synthetic linear polyamide fabrics by steam treatment. While such treatment does improve the ability of the fibers to recover from deformation and, when applied to fabrics, decreases their tendency to wrinkle, it brings about only a small improvement in the resilience of the fabric. Furthermore, the process requires a long treatment and therefore does not lend itself to continuous operation.

An object of this invention is to bring about a permanent improvement in the properties, particularly in the resilience, of fabrics prepared from synthetic linear polyamide fibers. ject is a new and improved process for setting the weave or stitch in such fabrics. A further object is a treatment which brings about these improvements in properties very rapidly and which, therefore, can be applied on a continuous and economical basis ,for large scale operation. Other objects will appear hereinafter.

'I'hese objects are accomplished'by a treatment, more particularly described hereinafter, in which a fabric comprising synthetic linear polyamide bers is' uniformly heated for a short time to a temperature closely approaching the fusion point of the fibers. To effect rapid transfer of heat to the fabric and to minimize the danger of oxidation, the fabric is most advantageouslyheated by bringing it in contact with a heated surface. To obtain a uniform product, the fabric as originally treated mustbe uniform with respect to its content of moisture or other swelling agents.

The term fiber is used herein to include both short (staple) and long (continuous) filaments.

The process of this invention is most advantageously applied 'at-that stage in the processing of the fabric Where nishng treatments would Another ob# normally be applied. The process is applied to fabrics in which the stitch or weave has not yet been set, or has been but partially set, and constitutes a new step in the manufacture of the fabric for submission to the trade.

This invention is of particular value in connection with woven fabrics and will therefore be described with reference to such fabrics. While the process may be applied directly to the fabric as it comes from the loom, it is preferably applied to the fabric after it has been given a washing or boil off treatment. Such prior treatments serve to remove yarn sizes, oils, etc., which may be required in the Weaving processes. Under the boil ofi' conditions, the weave of the fabric is not set, or at least only partially set, so thatthe fabric is left in a favorable state for application of the present process.

After the fabric has been washed it is put in condition for the heat treatment. If the fabric is to be treated in the moistl condition, the fabric is run through squeeze rolls or the like to remove excess water. This will give a fabric of uniform moisture content which can be heat treated directly. On the other hand, if it is desired to treat the fabric dry or to incorporate specific amounts of water or other swelling agents, the fabric is dried or partially dried and the desired amount of swelling agent added. It is essential that the fabric be uniform with respect to water content or content of other swelling agents, plasticizers and the like, if a uniform effect is to be produced in the heating operation.

The heating opera-tion consists in bringing the fabric for a short time to a temperature closely approaching the fusion point of the fabric. This is preferably done by passing the fabric over a heated surface or between two heated surfaces under pressure since this brings about almost instantaneous heating of the fabric to the desired temperature and avoids long exposure to heat such as occurs when the fabric is heated in an oven. As will be more fully explained hereinafter, the temperature to which the fabric is heated will depend upon the melting point of the polyamide, the amount of water or other modifying agent present, and the manner in which the heat is applied.

Fig. 1 is a diagrammatic view in elevation of one form of apparatus for carrying out my invention, and

Fig. 2 is a similar view of a modified apparatus.

The fabric and the heated surface can be brought in contact by various methods. A1- though the fabric can remain stationary and the heated surface moved over the fabric, it is generally more convenient to draw the fabric across the heated surface. Thus the fabric can be carried past the heated surface by means of a belt, or can be drawn or carried over a heated roll or rolls with or without pressure being maintained on the back of the fabric. Likewise the fabric can be heat treated by a roll pressing the fabric against a heated shoe or .by numerous other devices.

In the process as carried out by the mechanism of Fig. 1, the fabric after being given a preliminary boil off to remove the size and oil used in weaving is rinsed free of soap, dyed if desired, and wound on the supply roll S either before or after drying, depending upon the condition in which the fa-bric is to be processed. If the fabric is to be processed dry, i. e. in equilibrium with air at a definite humidity, the fabric is air dried before winding and the fabric brought to equilibrium with the air on the roll. If the fabric is to be heat treated in the wet or damp state, it can best be wound on the supply roll before drying, thus avoiding the necessity for subsequent water treatments. For treatments with swelling agents, the fabric is preferably dried before such treatments to insure uniform and controllable take up of the swelling agent. For prolonged contact of swellingagent with fabric, the fabric is best passed through the swelling bath before winding on the lsupply roll. and then allowed to remain on the roll for some time to insure uniformity. When ready for heat treatment, the supply roll S containing1 the fabric is placed in the position shown in the drawing. If the fabric is to be treated as such, the bath B is omitted, the fabric being passed directly over the guide G3 and between the rolls P1 and P2 to the wind-up roll W. Either one or both of the rolls P1 and P2 are equipped so that they may be heated and their surfaces maintained at an accurately controlled and uniform temperature. The fabric is carried through the equipment by synchronized driving mechanism on the heater rolls Pi and/or P2 and the wind-up roll W. If the fabric is to bev treated with a liquid prior to the heat treatment, the bath B is used, the fabric being run under the guides G1 and If desired, the bath can be replaced by a spray or other device for applying the liquid uniformly to the fabric. It is desirable that one of the rolls P1 or P2 have a surface of a soft porous structure, for example, a heavy fabric. The type of equipment shown in Fig. 1 is particularly desirable where high pressures are applied to the fabric and where extremely brief contact times are desirable. Greater contact times of fabric with heated roll can be maintained without reduction in roll speed by raising the position of the guide G3, to give a larger area of contact with the roll. This has the further advantage that the fabric is largely shrunk before passage through the rolls which lessens the tendency for wrinkling to occur between the rolls.

The equipment illustrated in Fig. 2 is identical with that shown in Fig. l except for the means for applying heat and pressure to the fabric. The heating and pressing are accomplished by passing the fabric between the roll H and the split cylinder or shoe P. The split cylinder makes possible the application of sufficient pressure to insure adequate metal to fabric contact. The equipment may be arranged so that either the roll or the cylinder or both can be maintained at a uniformly controlled elevated temperature. As in Fig. l, the bath B can be eliminated or a spray substituted for it.

The heat processed fabric may, if desired, be washed or treated with special nishes before submission to the trade. Such treatments or nishes are, however, merely supplementary and contribute no fundamental changes to the processed fabrics, which have been permanently improved by the -basic process of this invention. In cases where the heat stability of the nish permits, the finish can be applied before the fabric is subjected to the heat treatment of this invention.

The invention is illustrated more specifically in the following examples.

EXAMPLE I A satin fabric woven from polyhexamethylene adipamide yarn (M. P. in air about 250 C.) was boiled offat 70 C. in a dilute soap solution to remove the size, oil, etc. used in the weaving aseaoer operation. The fabricwas then dried and allowed to reach equilibrium in an atmosphere of 65% relative humidity. The fabric was next heat processed for 6 seconds by passing it between a metal shoe maintained uniformly at 240 C. and afabric covered driving roll, maintaining a pressure of 1 pound per square inch. The finished fabric possessed negligible residual shrinkage, was permanently set, and had an attractive appearance, good hand, resilience andv drape.` A similar fabric, processed at 200 C.. also had satisfactory properties, Whereas one processed at 150 C., while superior to the above satin fabric, was still to be classed as an unfinished product.

Measurement of the crease angle of a fabric serves as a quantitative measure of its resilience. The crease angle is determined by folding a one inch square of fabric so that in separate tests both the Warp and filling threads are bent through 180,placing a 1 kilogram weight on the folded fabric for 1 minute and measuring the 'angle to which the fabric recovers 30 seconds after removal of the weight. The crease angle is the angle which the fabric lacks of flattening out, the smaller the crease angle the better the resilience. Resiliences of the above satin fabrics in terms of the crease angle, as determined by. this method, are given below.

Percentage f Creasc decrease lemperature used m treatment angle in crease angle Degrees No treatment (control) 54 0 200 G .l 20 63 240 Gy 16 70 The treated fabrics of this invention are distinguished from like fabrics not receiving the present treatment by a greater resilience. Although the resilience depends somewhat upon the fabric structure, the treated fabrics of this invention for the most part have a crease angle, as defined above, of less than 25.

While a difference in crease angle of a few degrees may seem small, it makes a significant difference in the hand of the fabrics. A marked difference in resilience exists between the fabrics treated at 200 C. and 240 C., and a great difference between the fabrics treated at 150 C.

and 240 C. The preferred temperatures for treatment under the above conditions lie between 220 and 245 C.

EXAMPLE II A fabric prepared from 90 denier, 30 filament polyhexamethylene adipamide yarn woven with 103 warp and 71 filling ends per inc-h was desized by agitation in lukewarm water and air dried. This fabric, when soaked or dipped in a saturated aqueous solution of benzyl alcohol and then heated uniformly over its ,entire width'by means of a surface maintained at a temperature between 210 and 240 C. was of good appearance, hand, drape, and resilience. The crease angle of the treated fabric was 15 which was 62% less than that of the original fabric.

Benzyl alcohol, a high boiling liquid dissolves polyamides at its boiling point (205 C.) but when used in aqueous solution (preferably less than 5% benzyl alcohol) is effective in promoting setting of polyamide fabrics at lower temperatures than possible without the active agent. The quantity of solvent used is insufficient to dissolve the fibers, yet sufficient to render them fusible at somewhat lower temperatures. Likewise effective are other solvent or swelling compositions, such as aqueous or alcoholic solutions of phenols, gly cols, acids, alcohols, and the'like. Whereas alcohols and phenols tend to produce softer fabrics of improved drape, the more active acids. such as formic, tend to give a crisper feeling product. Swelling compositions are particularly effective when it is desirable to use lower heating temperatures or in refinishing fabrics previously heat setwhere the added softening effect of the solvent enables the fibers to be more readily reset than when dry or water saturated.

EXAMPLE IV The following table gives the results obtained by bringing a moist polyhexamethylene adipamide fabric in contact with a uniformly heated smooth surface under a pressure of about 2 pounds per square inch.

At the pressure indicated the optimum surface temperature lies between 220 and 235 C. At this temperature a contact time of 6 seconds is sufficient.

EXAMPLE V A moist fabric of polyhexamethylene adipamide, while supported on a canvas belt, was drawn over a stationary roll heated to 260 C. Under these conditions the entire width of the fabric was pressed lightly against the surface of the heated roll. After two passages over the roll with a contact time of 2 seconds for each pas sage, the fabric was found to have a crease angle of 22.

That plate temperatures approaching the melting point of the polyamide are most effective has been shown in the previous examples where relatively low pressures (2 pounds per square inch and less) were used to promote contact of the fabric with the heated surface. When high pressures are used, the temperature is more critical, particularly when the fabric contains a swelling agent. With high pressures lower temperatures must be used and the times of contact must be extremely brief as is illustrated in the following example Where the effect of pressure is particularly considered.

EXAMPLE VI A woven polyhexamethylene adipamide fabric was soaked in water. superficially dried to remove surface water, and then pressed under high pressure against a heated copper surface for an accurately timed period. The results obtained by treating several samplesof fabric in this manner showed that the best results were obtained at a temperature of about 200 C. with a contact time of,0.1 to 0.2 second. Longer contact at this temperature resultedjn a weakening of the fabric. The crease angles of the products treated for 0.1 to 0.2 second ranged from to 11. In contrast a like fabric treated in an autoclave for 4 hours in saturated steam at 140 C. had a crease angle of It should be noted that the present treatment is acco plished in a very small fraction of the time requ ed for the steam treat` ment and produces a greater improvement EXAMPLE VII A fabric was woven from yarn spun from a polyamide (M. P. in air about 285 C.) derived from p-bis (beta-aminoethyl) benzene and sebacic acid. After the fabric was soaked in water to remove the size and given a boil-off with 2% soap solution, the moist fabric was effectively treated by bringing it in contact for 10 seconds with a plate maintained at 250 C. The finished fabric had a crease angle of 15 as compared to 54 for the original desized fabric.

EXAMPLE VIII A sample of polyhexamethylene adipamide yarn is woven into a fabric with a 120 x 70 construction. The fabric is given a boil-off treatment and/is then wound on a receiving roll. The fabric is unwound from this roll, passed under a ,guide roll partially submerged in a trough of water, and then passed between two heatedpinch rolls. After passing through the pinch rolls, the fabric is collected on a Wind-up roll. The pinch rolls are electrically heated to a temperature of 195 C. and thermostatically controlled so that s the temperature of the rolls remains within the range 19o-200 C. The pressure between the rolls is adjusted t0 give good roll-to-fabric contact. The Wind-up roll is driven at such a speed that the fabric passes through the pinch rolls at a rate of 4 yards per minute.

The crease angle of the finished fabric was 18 as compared with 45 for the fabric after the boil off.

EXAMPLE IX A yarn spun from polyhexamethylene adipamide staple fibers which has been mechanically crimped by a stuffer-crimpingfprocess and which has not been subjected to any hot, wet setting condition is woven into a fabric. The fabric is given a boil-off treatment and is then wound on a receiving roll. The fabric ris then subjected to v a finishing treatment in accordance with Example VIII by unwinding the fabric from the roll, passing it through a trough of water, and then between two heated pinch rolls. The fabric is found to have a markedly increased resilience over that of a sample of the same fabric which was subjected to a conventional wool fabric iinishing treatment.

EXAMPLE X Polyhexamethylene adipamide is spun from melt into a 116 denier, l0 filament yarn. This yarn is doubled into a rope of approximately trade.

11,600 denier and is then cold drawn approximately 400% (ratio of drawn to undrawn, 4: 1) to :produce a drawn rope of approximately 3,000 denier. This rope' is then crimped by a gear crimping process which consists in pressing the superpolyamide filaments between intermeshing serrated racks and heating them in this position with steam, preferably saturated steam at 10D-150 C. The function of the steam is to make the crimp more permanent. The crimped filaments are then cut into staple, spun into yarn, and woven into a fabric suitable for the lproduction of a mans suit. The fabric is then finished at 240 C. in accordance with the method described in Example I. The fabric has a markedly better resilience than a, similar fabric processed at 150 C. When converted into a man's suit, the fabric maintains a smart, neatly pressed appearance even when subjected to rough use; whereas a similar fafbric which has only been finished according to a conventional wool fabric finishing method becomes wrinkled very easily and does not exhibit a resilience even approaching that of the fabric finished in accordance with this invention.

EXAMPLE XI A Sample of dyed satin fabric woven with 30 denier warp-40 denier filling thread structure was decatized by standard mill processes. The fabric was considered unsatisfactory by the When this fabric was treated in the air dry condition for 5 to 10 seconds at 230 C. by the process of Example I, its hand, drape, ap -pearance and resilience were markedly improved. The product was considered acceptable by the trade.

From the foregoing examples it will be seen that the resiliency of polyamide fabrics is greatly improved by bringing the fabrics in contact with a heated/surface under proper conditions. Other propertiesimprove'd are the draping qualities and hand of/the fabrics. Although the exact cause for these improvements has not been established definitely, it is believed that the treatment of this invention softens (without fusing) the fibers sufficiently to relieve strains introduced vin the sets the yarns in this relaxed condition which is in conformity with the desired weave pattern of the fabric. Examination of finished fabric shows that both the warp and filling yarns have taken on a permanent set. tersection in the weave the yarns are set in the form of humps. This permanent setting of the yarns in conformity with the weave/appears to be essential to good fabric properties.

The process is preferably appliedy before the fabric is formed into garments or sold to the trade since untreated polyamide fabrics are particularly subject to weave distortion, permanent wrinkling, creasing and the like. However, due to the fact that the treatment of this invention makes it difficult to form sharp creases in the finished fabric, garments in which sharp and permanent creases are of prime importance may be made from untreated fabric and the heat treatment applied to the garment, In this way shaped or formed articles of apparel can be formed from the fabric.

As compared with the finishing treatments which are applied to fabrics made from other types of fibers, e. g. silk, wool and rayon, the

At the points of intreatment herein described for the polyamide fabrics is unusually severe with respect to the temperatures used. The process of this invention, when applied to fabrics of these other types of fibers, do not have the beneficial effects they do in the case of the synthetic polyamide fabrics.

The process of this invention is further characterized in that its effect is essentially permanent. Subsequent treatments, such as fabrics receive in further processing and use, e. g. hot dyeing and laundering, do not destroy the benecial effect of the finishing treatment. The effect is permanent even at elevated temperatures. For example, if a sharp crease is introduced into a polyamide fabric by the process of this invention, this crease persists through laundering and is not completely removed even by ironing. In contrast creases in similar silk or wool fabrics are completely eliminated by washing and ironing.

With further reference to the severity of the conditions in the process of this invention, it may be pointed out that although the fibers undergo shrinkage they retain their orientation. However, there may be some change in the fiber structure since the dyeing properties of the fabrics are altered by the process. The finished fabrics dye uniformly but less deeply than untreated fabrics, both with acid and Celanthrene type dyes.

In the foregoing examples the polyamide fabrics were pretreated in various ways before they were subjected to the heating operation. For wet treatments it is often desirable to soak the fa-bric in water for several hours before the heat treatment, removing the excess surface moisture just before applying the heat treatment. It is also permissible to boil the fabric for a brief period in water, soap solutions, or other textile processing baths including the milder swelling baths prior to the finishing treatment. It has been found that boiling the fabric in an aqueous solution of a water-soluble polyamide, e. g. that derived from triglycoldiamine. and adipic acid, serves to give a fabric which finishes particularly well in the subsequent heat treatment. This is apparently due to impregnation of the fabric with the lower boiling water-soluble polyamide. It is frequently advantageous to partly preset a polyamide fabric by plunging it into boiling water or soap solution while maintaining the fabric smooth and to its full width, since this presetting serves to minimize wrinklng, creasing, or detorsion of the fabric in any subsequent operations carried out prior to the final heat treatment.

Although these pretreatments in themselves have some setting effect on the fabrics, they do not interfere with the subsequent treatment of this invention which is carried out at a much higher temperature.

The finish desired on the ultimate fabric determines to a considerable extent the pressure to be used in contacting the fabric with the heated surface. In order to obtain softl fabrics, low pressures are necessary, pressures of from a fraction of a pound to several pounds per squareV inch being most effective. While the invention is most advantageously applied by treating the fabric o'n a heated surface since this process insures rapid heat transfer and does not contaminate the fabric, some degree of success has been achieved by heating the fabric in other ways. For example, the fabric may be passed through a hot inert liquid or the fabric may be passed through a zone in which it is heated by infra red radiations.

The temperature used in the heating step will generally be within about 5 to 25 C. of the temperature causing fusion or visible damage to the fabric. The temperature employed in a given case depends upon the particulal polyamide iiom which the fabric is made, the amount, if any, of water or other swelling agent present in or on the fibers, and the pressure applied to the fabric. rlhus, for dry fabrics made from polyhexamethylene adipa'rnide, which melts at about 2b0 C. on a metal block in air, plate or sullace temperatures in the neighborhood oi 22m-2&0 C. are particularly effective when pressures in the neighborhood of one pound per square inch are used. For polydecametnylene adipallliiie iaorlcs, which melt at about 22o C. the temperature should be correspondingly lower. When the fibers contain swelling agents, lower linisnliig temperatures are employed than in tneabsence of swelling agents, since the swelling agent lowers the fusion point of the fibers. For example, under pressure polyamides become soluble in water at temperatures well below the melting point of the dry polymer. The actual `melting point lowering depends upon the moisture content of the polyamide and ior certain polyamides may amount to 50 C. ln heating a water saturated fabric two phenomena which occur are a gradual elimination of water and a gradual rise in the temperature of the moist fibers. If the rate of heating is not too rapid, the water can be removed before the polymer melting point is reached and temperatures within about b C. or' the dry polymer fusing point can be used safely. 1f heat is rapidly applied, as'by contacting the fabric with a heated surface or plate under considerable pressure, plate temperatures as much as bo C. below the dry polymer fusing point may be excessive. For polyamide fabrics containing other swelling agents, which include certain compounds per se, particularly non-solvents containing hydroxyl groups, and also mixtures of lpolyamide solvents and non-solvents, the .behavior ls similar to the effect with water except except that for the less volatile or more active agents slower rates of heating or lower temperatures must be used. Plate temperatures about 52U C. Ibelow the fusion point of the fabric are most effective. It should be noted, however, that these temperatures, depending upon vthe pressure applied during the treatment and the nature and amount of the swelling agent, may range from about 20 to "i0Q C. below the melting point of the dry polymer. However, it is essential that the temperature employed be maintained uni'- formly over the heated surface with a maximum fluctuation not exceeding 10 C. if truly uniform products are to be obtained. Furthermore, in order to obtain the full advantage of the process of this invention, 'conditions should be chosen so that the temperature of the heated surface can be 190 C. or higher. For this purpose all of the polyamides disclosed herein have melting or fusion points of at least 200 C.

The time of contact between the fabric and the heated surface should be sufficient to bring the fabric to the desired temperature but insufficient to permit significant damage to the fabric by oxidation. The time of contact will generally be less than one minute and in most cases from a fraction of a second to 15 seconds. Maximum changes in fabric properties occur during the rst few seconds of heating with but slight additional improvement over the next minute. In

the case of fabrics which are particularly sensitive to oxygen, it is desirable to effect the finishing operation in an inert atmosphere, e. g. nitrogen or carbon dioxide. Although there is considerable latitude in the conditions of temperature, pressure, and time of contact which can be employed in the finishing treatment, it will be apparent that these variables are interdependent. Furthermore, it should be emphasized that it is very important that the temperature, pressure, and time of treatment be kept essentially constant during the treatment of a given piece 'i of fabric if a uniform product is desired.

Polyamide yarns and fabrics shrink extensively on heat treatment, the amount of shrinkage d pending upon the initial condition of the fabric, i. e. whether dry, moist with water or other swelling compositions, and on the rate and method of heat application. To eliminate serious future shrinkage, and give a smooth uniform fabric homogeneous in physical properties, it is essential that heat be applied uniformly over the full width of the fabric and that the fabric be uniform with respect to content of water or other swelling composition. Failure to apply the heat treatment simultaneously and uniformly over the full width of the fabric leads to an unsatisfactory product. When the heat treatment is applied over only a portion of the width of the fabric the moisture content and other properties of the fabric change through asharp gradient at the junction of the heated and non-heated portions. This causes puckering of the fabric due to shrinkage of the heated area. A second heat treatment overlapping the first fails to remove completely this puckering at the gradient area.

The invention is broadly applicable to fabrics made from polyamide fibers. As additional examplesl of polyamides may be mentioned polytetramethylene suberamide, polytetramethylene sebacamide, polypentamethylene adipamide, polyhexamethylene sebacamide, polydecamethylene p-phenylene diacetamide, poly-p-xylylene sebacamide, and G-aminocaproic acid polymer.

The term polyamide" as used herein includes interpolyamides and also interpolymers which contain other linkages in addition to amide linkages, such as those obtained by including with the polyamide-forming composition from which the polymer is prepared other linear polymerforming reactants. Examples of polyamides of this kind are the ester-amide interpolymers.

It is not necessary that the fabrics consist solely of polyamide fibers. The fabrics may be prepared from yarns containing other fibers in addition to polyamide fibers or from polyamide yarns and other types of yarns. The other fibers or yarns should, however, have sufficient thermal stability to withstand the finishing treatment. The best results are obtained with fabrics consisting largely of polyamide fibers. It is also possible to use fabrics made from two or more different polyamides or from fibers spun from a mixture of polyamides. The fabrics'l may be of the woven, knit or felt types.

The polyamide fibers present in the fabric may contain modifying agents, such as plasticizers, e. g. phenols or aryl sulfonamides, delusterants, e. g. titanium dioxide, pigments, extenders, fillers, dyes, resins, antioxidants, oils, and cellulose derivatives. The fibers may be long, i. e. continuous, or short, i. e. staple fibers. The fibers may be crimped or uncrimped. When crimped fibers are used, they may be the products of mechanical crimping processes, such as stuffer-crimping or such as described in U. S. Patent 2,'197,896;. or of spontaneous crimping processes, such as are described in U. S. Patent 2,174,878 and in copending applications Serial Numbers 183,922, now Pat. No. 2,287,099, 233,481, now Pat. No. 2,249,756 and 324,847 now Pat. No. 2,296,202; or of bale-crimping processes, such as described in copending application Serial No. 232,470 now Pat No. 2,217,113. The crimp may be rendered more permanent by a mild setting treatment with a hydroxylated non-solvent swelling agent. However, this is not necessary since the crimped bers can be spun into a yarn and fabricated without losing an appreciable amount of their crimp.

This inventionl as will be apparent from the foregoing description, provides a rapid and economical process for improving permanently the resilience, drape, and hand of fabrics prepared with the use of synthetic linear polyamide fibers. Although the process is a simple one, the operating conditions must be carefully controlled and for this reason the process is preferably applied as a finishing treatment to the fabric before it is submitted to the consumer and in all cases before it has left the hands of an experienced and. properly equipped operator.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to' be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

1 claim:

1. A process for treating fabric comprising synthetic linear polyamide fibers having a fusion temperature of at least 200 C. to set said fabric and impart thereto improved resilience and a crease resistance which are not destroyed by subsequent laundering and ironing, said process comprising a step in the manufacture of the finished fabric for submission to the trade which comprises heating the polyamide fabric uniformly and simultaneously over its entire width by pressing the fabric over its entire width against a heated surface and under essentially constant pressure between the fabric and heated surface until the temperature of said fabric is at least C. and within the range of 5r to 25 C. below the fusion point of said polyamide fibers, and discontinuing said heating before the fabric has been weakened substantially.

2. A process for treating .fabric comprising synthetic linear polyamide fibers having a fusion temperature of at least 200 C. to set said fabric and impart thereto improved resilience and a crease resistance which are not destroyed by subsequent laundering and ironing, said process comprising a step in the manufacture of the finished fabric for submission to the trade which comprises heating the polyamide fabric uniformly and simultaneously over its entire width by continuously passing the fabric over a heated surface with an essentially constant pressure of the fabric against the heated surface and with a time of contact of fabric and heated surface' which heats the fabric to a temperature of at least 190 C. and within the range of 5 to 25 C. below the fusion point of the polyamide fibers.

3. A process for treating fabric comprising synthetic linear polyamide fibers having a fusion temperature of at least 200 C. to impart to said fabric an improved resilience and a crease resistance which are not destroyed by subsequent laundering, said process comprising the steps in the manufacture of the finished fabric for submission to the trade which consists of uniformly treating said fabric with a swelling agent and then heating the treated fabric uniformly and simultaneously over its entire width by pressing the fabric over its entire width against a heated surface and under essentially constant pressure between the fabric and heated surface until the temperature of said fabric is at least 190 C. and with the range of D to 25 C. below the fusion point of said polyamide fibers, and discontinuing said heating before the fabric has been weakened substantially. l

4. A process for treating fabric comprising synthetic linear polyamide fibers having a fusion temperature of at least 200 C. to impart to said fabric an improved resilience and a. crease resistance which are notl destroyed by subsequent laundering, said process comprising the steps in the manufacture of the finished fabric for submission to the trade which consist of uniformly treating said fabric with water to bring the fabric to a uniform moisture content substantially below the saturation point, and then heating the treated fabric uniformly and simultaneously over its entire width by pressing the fabric over its entire width against a heated surface and' under essentially constant pressure between the fabric and heated surface until the temperature of said fabric is at least 190 C. and within the range of 5 to 25 C. below the fusion point of said polyamide fibers, and discontinuing said heating before the fabric has been weakened substantially.

5. The process set forth in claim 1 inl which said polyamide fibers are polyhexamethylene adipamide fibers and in which the fabric is heated in an essentially dry state for a period not exceedlng one minute in close contact with a surface having a temperature between 220 C. and 245 C.

6. In a process for obtaining a fabric woven from synthetic linear polyamide fibers having a fusion temperature of at least-.200 C. and characterized by an improved resilience and a crease resistance which are not destroyed by subsequent laundering and ironing, the'steps in the manufacture of the finished fabric for submission to the trade which comprise treating the fabric, after it has been removed from the loom, to remove the size, oils and the like, and then before the weave in the fabric has been completely set, heating the fabric uniformly and simultaneously over substantially its entire width by pressing the fabricl over substantially its entire width against a heated surface and under essentially constant pressure between the fabric and heated surface until the temperature of said fabric is at least C. and within the range of 5 to 25 C. below the fusion point of said polyamide fibers. and discontinuing said heating before the fabric has been weakened substantially.

7. A fabric which comprises essentially polyamide fibers, and which has a crease angle of less than 25, and -Which is obtained by the process set forth in claim 1.

8. The process set forth in claim 3 in which said polyamide fibers are polyhexamethylene adipa'mide' fibers.

9. The process'set forth in claim 4 in which said polyamide bers are polyhexamethylene adipamide fibers.

ERNESTB. BENGER. 

